Arresting Bed Degradation in the Waal River: Intervention strategies

The upper Dutch Rhine branches show continuous bed degradation (1-2 cm/year) threatening multiple river functions. The bed degradation is a response to past sand mining, channel narrowing and straightening, which increased sediment transport capacity and created a sediment transport gradient that drives ongoing erosion (Figure 1). Room for the River 2.0 (RftR 2.0) aims to create a climateresilient river system, supporting river functions. Arresting bed degradation is essential to prevent further deterioration of river functions. For the Waal River, two principal intervention strategies were investigated: (1) continuous sediment management and (2) a large-scale implementation of the multi-channel approach. While sediment nourishment counteracts ongoing erosion by supplying the deficit in the sediment balance, the multi-channel approach reduces sediment transport by diverting discharge from the main channel to a parallel side channel. The objective of this abstract is to determine the effectiveness of both interventions in arresting bed degradation. We present the results of the intervention strategies evaluated with a quasi-3D morphodynamic model (Delft3D) in which the multi-channel approach is schematised as longitudinal training walls separating a side channel from the main channel.